Free IBAN API – Validate & Calculate German IBANs

Validate an IBAN

POST /api/v1/validate

Checks any IBAN for length, country format and the ISO 7064 MOD-97 check digit. For a German IBAN it also resolves the bank name, BIC and BLZ from the Bundesbank directory.

{
  "iban": "DE89370400440532013000"
}

curl -X POST https://www.iban-rechner.pro/api/v1/validate \
  -H "Content-Type: application/json" \
  -d '{"iban":"DE89370400440532013000"}'

const res = await fetch("https://www.iban-rechner.pro/api/v1/validate", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ iban: "DE89370400440532013000" }),
});
const data = await res.json();

{
  "valid": true,
  "iban": "DE89 3704 0044 0532 0130 00",
  "country": "DE",
  "sepa": true,
  "sepaInstant": null,
  "bank": "Commerzbank Nürnberg",
  "bic": "COBADEFFXXX",
  "blz": "37040044"
}

A structurally invalid IBAN also returns HTTP 200 with valid: false and an error message — the request itself was well-formed:

{
  "valid": false,
  "iban": "DE00 3704 0044 0532 0130 00",
  "error": "Invalid check digits"
}

sepa and sepaInstant are true, false or null. null means the public BLZ dataset does not prove scheme reachability either way — it is not a negative. The bank, bic and blz fields appear only when the bank code is found.

Calculate a German IBAN

POST /api/v1/calculate

Builds a German IBAN from a bank code (BLZ) and an account number. Only country: "DE" is supported — the BLZ + account scheme is Germany-specific. The BLZ must exist in the public Bundesbank register.

{
  "country": "DE",
  "blz": "37040044",
  "account": "0532013000"
}

curl -X POST https://www.iban-rechner.pro/api/v1/calculate \
  -H "Content-Type: application/json" \
  -d '{"country":"DE","blz":"37040044","account":"0532013000"}'

const res = await fetch("https://www.iban-rechner.pro/api/v1/calculate", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    country: "DE",
    blz: "37040044",
    account: "0532013000",
  }),
});
const data = await res.json();

{
  "iban": "DE89 3704 0044 0532 0130 00",
  "valid": true,
  "formallyValid": true,
  "assurance": "mathematical-only",
  "warning": "Standardformel; bankspezifische Bundesbank-IBAN-Regeln …",
  "bank": "Commerzbank Nürnberg",
  "bic": "COBADEFFXXX"
}

The response carries assurance: "mathematical-only". The IBAN is built with the standard MOD-97 formula, which is correct for the large majority of German banks. A minority of institutions use deviating Bundesbank IBAN rules that are not published in the public BLZ dataset, so a mathematical-only IBAN should be reconciled against your bank records before you rely on it. That is exactly what the warning field states (in German).

Error responses

Errors return a JSON body with an error string and one of these status codes:

Limits & fair use

• •No authentication and no SLA. This is a best-effort free service with no uptime guarantee. Do not build anything mission-critical directly on it.
• •Request bodies are capped at 4 KB. Larger bodies return 413.
• •No rate limit is currently enforced, but fair use is expected. If you need high or sustained throughput, please self-host rather than hammering this endpoint.
• •calculate returns assurance: "mathematical-only" because some banks use deviating Bundesbank IBAN rules that are not in the public BLZ dataset. Treat the result as formally valid, not bank-confirmed.